dart2js: Introduce HGetLength to replace strange use of HFieldGet

pkg/compiler/lib/src/ssa/builder_kernel.dart

Index: pkg/compiler/lib/src/ssa/builder_kernel.dart
diff --git a/pkg/compiler/lib/src/ssa/builder_kernel.dart b/pkg/compiler/lib/src/ssa/builder_kernel.dart
index cd0532bece1f486f692064758d78846aaac2e0ad..551be940de95cc5fc71ebac2af93ba7facf3ba05 100644
--- a/pkg/compiler/lib/src/ssa/builder_kernel.dart
+++ b/pkg/compiler/lib/src/ssa/builder_kernel.dart
@@ -754,8 +754,7 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
     HInstruction originalLength = null; // Set for growable lists.
 
     HInstruction buildGetLength() {
-      HFieldGet result = new HFieldGet(
-          astAdapter.jsIndexableLength, array, commonMasks.positiveIntType,
+      HGetLength result = new HGetLength(array, commonMasks.positiveIntType,
           isAssignable: !isFixed);
       add(result);
       return result;
@@ -2627,7 +2626,7 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
   }
 
   HInstruction _buildInvokeSuper(
-       ir.Expression invocation, List<HInstruction> arguments) {
+      ir.Expression invocation, List<HInstruction> arguments) {
     // Invocation is either a method invocation or a property get/set.
     // TODO(efortuna): Common interface?
     // TODO(efortuna): Add source information.
@@ -2642,9 +2641,9 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
     inputs.add(receiver);
     inputs.addAll(arguments);
 
-    ir.Member interfaceTarget = invocation is ir.SuperMethodInvocation ?
-        (invocation as ir.SuperMethodInvocation).interfaceTarget :
-        (invocation as ir.SuperPropertyGet).interfaceTarget;
+    ir.Member interfaceTarget = invocation is ir.SuperMethodInvocation
+        ? (invocation as ir.SuperMethodInvocation).interfaceTarget
+        : (invocation as ir.SuperPropertyGet).interfaceTarget;
 
     HInstruction instruction = new HInvokeSuper(
         astAdapter.getMember(interfaceTarget),